Many types of electronic components and circuits require a nonplanar substrate surface. For example, in the field of optoelectronics, channels are often etched on the surface of a silicon substrate in order to provide mounting of optical components or to increase coupling efficiency between the components. (See, e.g., U.S. Patent Application of Anigbo et al, Ser. No. 60/009116, filed Dec. 22, 1995, which is incorporated by reference herein.) In many cases, these nonplanar surfaces require a metal coating which, for example, acts as a reflecting layer. Since these metal layers are usually patterned, a mask should be employed on the substrate surface. Typically, the mask employed for patterning metal on a planar substrate surface is a photoresist material. However, when the surface is nonplanar, difficulties can be encountered in depositing and cleaning off the photoresist material.
In the fabrication of planar integrated circuits, it is known in general to employ masks made of metal (e.g., molybdenum) on the substrate, a technology usually referred to as shadow masking. This technique has lost favor in the industry due to the inability to achieve accurate registration.
It is desirable to provide a shadow mask technique which can be used for depositing metal on a nonplanar or planar substrate and achieve accurate registration.
It is known in general to position two components by forming conical bores in the facing surfaces and provide spheres in the bores. (See U.S. Pat. No. 4,070,120 issued to Bald et al.) It is also known to position silicon IC chips onto silicon or ceramic substrates by etching V-grooves in the substrate which correspond to contact pads on the chip having spheroidal solder or gold so that the solder or gold will be located within a corresponding groove. (See U.S. Pat. No. 3,379,937 issued to Shepherd and U.S. Pat. No. 4,288,808 issued to Hantusch.) It has been further suggested to position a ceramic chip carrier or a silicon chip on a printed circuit board by forming indentations in both the chip and substrate and employing spherical bodies in the indentations. The indentations can be pyramid shaped. (See, U.S. Pat. No. 3,184,831 issued to Siebertz, and U.S. Pat. No. 4,565,314 issued to Scholz.)
The art does not appear to have addressed the problem of how to deposit a metal onto a nonplanar or planar substrate by means of shadow masking to achieve accurate registration.